The present invention is directed to the field of microscopy, and more particularly to the field of high-resolution scanning microscopy.
Scanning microscopes generally function by focusing electromagnetic energy at a point location of a sample, collecting reflected or transmitted energy from the interaction of the incident energy with the sample, and repeating the procedure at an array of points over an area of interest on the sample. Common examples of scanning microscopes include the scanning electron microscope, in which the electromagnetic energy is in the form of an electron beam, and the confocal microscope, in which the electromagnetic energy is typically in the form of light in the wavelength range from ultraviolet to infrared.
A standard confocal microscope employs both source and detection “pinholes” (tiny openings in otherwise opaque screens) along with optics in order to illuminate and image only a very small area of a sample confocal to the pinholes, thus providing high resolution. The source pinhole helps to filter out stray source light that would land outside the confocal area, and the detection pinhole filters out gathered light that emanates from outside the confocal area. Together, the two pinholes serve to pass light from a small in-focus area in the sample and block light from out-of-focus areas. The in-focus area is scanned over the sample, and an array of pixel values are obtained over the area in order to build up a two-dimensional image.
One variant of confocal microscopy, referred to as “two-photon” microscopy, takes advantage of the detectability of a pair of photons that are absorbed by a fluorescent molecule simultaneously. The rate of such absorption is related to overall photon density, which is higher toward the central part of an incident stream of photons, and thus the effective size of the confocal area is reduced.
Other techniques for improving resolution are known that rely on so-called “entangled photons”, or photons having interrelated quantum states. Entangled photons may be generated by spontaneous parametric downconversion such as occurs in some nonlinear crystal materials for example. One example of this type of technique is referred to as “quantum microscopy”.